The following percent times whole problems are easy to figure out in your head.
30% * 90 = 27 50% * 50 = 25 40% * 80 = 32 20% * 30 = 6
40 * 25% = 40 x .25 ------ 200 80 ------ 10.00 200 * 75% = 200 x .75 ------ 1000 1400 ------ 150.00
Now you get to try a few for yourself.